I started doing a lot with low power devices (Arduino, BLE 4.0) and coin cells are a convenient power source. Lately I found out that there are even rechargeable coin cells. That's why I needed a charger. There are only a few models out there which were either expensive or I didn't trust the charge current (too high). So I made my own.
There are two charge modes:
- fast (45mA)
- slow (25mA)
Max charge current for a coin cell is usually between 80% and two third of it's capacity. So you could charge a 100mA coin cell with 80mA. I wanted to increase the lifetime of my coin cells and reduced the charge current. If you want to have different currents here is the equation to calculate R_SLOW/R_FAST:
mA = 1000 / R in kΩ
Power Management ICs / Power Supply Support
Forgot to update it here: The circuit is charging the coin cell but the led indicator does not work. I am not sure if it's because I got a cheap chip from Aliexpress or what else ... The circuit is almost the exact copy of the reference implementation from the data sheet. The charging LED is on all the time and does not turn off. However the chip is charging correctly. Once the cell is full the amperage going to the cell is almost zero.